Electron beam centering system



April 27, 1948. H. w. e SALINGER ETAL 2,440,490

ELECTRON BEAM CENTERING SYSTEM ozrrom luo mi Filed Nov. 6', 1946 INVENTORS HANS W. G. SALINGER ATTORNEY Patented Apr. 27, 1948 UNE'EED. STATES hATEN'i? Q-E Fli'CE ELECTRON BEAM CENTERINGSYSTEM Hans W; G. Salinger and Albert T; Mayle, Jr., Fort Wayne, Ind, assignors, by mesne assignments, to Farnsworth,ResearchCorporation, a. corporation of Indiana Ap piicationNovcmber 6, 1946, Serial No. 708,004

7 Claims. 1

This invention relates to systems for controlling an electron beam and has particular reference to voltage distributing systems for impressingbeam orienting voltages on the field producing' electrodes of a cathode raytube.

According to conventional practice, wherever it is desired to deflect an electron beam over a target electrode, it isnecessary, not only to produce a field of substantially uniform intensity which is varied periodically in magnitude to efiect the desired beam deflection, but also to produce a second relatively constant field of uniform intensity, soa s to suitably orient the beam relative to the target electrode. Usually the field-producing facilities of thetube have impressed thereon substantially constant unidirectional voltages or currents in suitable magnitudes to produce the beam-orienting field. 'In addition these field-producing facilities have impressed thereonthe deflectingvoltages or currents, which in a sense, are superimposed upon the constant unidirectional voltages or currents.

Where. the cathode ray tube is one such as a television image dissector the electron beam has a cross-section of. considerable magnitude. Heretofore, it has been the general practice to orient and-deflect such a beam relative toa target electrode by means of electromagnetic fields. However, it also has been proposed to produce such a field electrostatically. One such device operating on this latter principle, is disclosed in Patent No. 2,297,949, granted to P. T. Farnsworth onOctober 6, 19.42, for a Defiecting system. In one embodiment of the patented structure, the field-producing electrodes; are in. the form. of elongated rods or stiff Wires, a number of which are placed in spaced positions around the path of the beam so that each of the electrodes extends generally longitudinally of the electron beam path. The.

high frequency and low frequency deflecting voltages are impressed upon these.- electrodes by means of a voltage distribution network of such a character that each of the electrodes has impressed thereon a voltage which in magnitude is proportional to the voltages impressed upon the other electrodes in accordance with its particular location relative to two coordinate scanning directions. The voltage distributin network is energized by the two deflecting voltages which vary periodically in magnitude according to the particular scanning pattern desired. Usually for analyzing a television image the deflecting voltages have substantially saw-tooth wave forms.

Ina device such as that disclosed in the Farms-- worth patent referred to, the so-called centering 2; voltage or the voltage by means of which the electron beam is suitably orientedreiative to the target electrode most conveniently is impressed.

upon the elongated field-producing electrodes. Inasmuch as the field'whi'ch it is desired toproduce for orienting the beam relative to the targetelectrode is not required to vary in its intensity,- the centering voltages impressedupon theelectrodes are unidirectional voltages of relatively constant magnitude. These centering voltages must also be impressed upcn the respective electrodes in suitable magnitudes according to the location ofthe electrodes relative to the direction of the beam-centering field in order that this.

of input terminals. in orderto shift the electron beam in one coordinate direction. avoltage. vary.- ing device isrequired between the source. ofen.- ergy for the distributionv network and one pair of. input terminals, and a similar device is re-,

1 quired for the other. pair-0t input terminals. Re.-

gardless of whether-one or twosources of energy are used to energize such a distribution network, there is a considerable power loss inherent in the operation of sucha system.

It is, therefore, one. ofv the objects of thisinvention to provide a novel voltage distribution. system fororienting an electron beam of a cathode raytuberelative to a target electrode with a. minimum loss of power. I

Another object of the invention is, to provide. an electron beam-centering voltage distributing system which utilizes only one relatively simple network.

Still another object of the invention is to provide a. novel system for centering an electron beam which. functions on a polar rather than a rectilinear coordinate basis.

In accordance with the present invention, there is provided a cathode ray'tube. which has facilities for developing an. electron beam and direct- Such a. system requires that thevoltage. distribution network be energized. at two. pairs ing it toward a target electrode. The tube also is provided with a plurality of field producing electrodes located in spaced positions around the path of the beam. These electrodes, when energized by suitable voltages in accordance with the invention, produce an electrostatic field of substantially uniform intensity and constant magnitude, whereby the beam normally is directed toward a predetermined point on the target electrode. The voltages for eiiecting the production of the beam-orienting field are impressed upon the electrodes by a voltage distributing network in accordance with an important feature of the invention. This network is designed so as to derive from a source of unidirectional voltage a predetermined voltage distribution pattern for the electrodes, whereby to provide a uniformly distributed field. The voltage distributing network is connected to the field-producing electrodes of the tube by means of a switch which is operable to effect a cyclical permutation of the electrodes with respect to the voltage distribution pattern, whereby to rotate the direction of the field about the longitudinal axis of the tube. There also are provided means for Varying the magnitude of the voltage by which the voltage distributing network is energized so that the strength of the field may be varied as desired.

For a better understanding of the invention, together with other and further objects thereof, reference is made to the following description, taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

In the accompanying drawing:

Fig. l is longitudinal sectional view of a television image dissector tube having a plurality of electrodes, whereby to effect electrostatic deflection of electron beam relative to a target electrode; and,

Fig. 2 is a schematic circuit diagram of apparatus embodying the invention, whereby suitable deflecting and centering voltages are impressed upon the tube deflecting electrodes.

Having reference now to Fig. 1 of the drawing, there is shown a television image dissector tube H. One end wall of the tube is provided with an optically plane window l2, and there is mounted adjacent to the other end of the wall of the tube a photoelectric cathode l3. The photosensitive surface of the cathode faces the window 12 so that an optical image may be projected through the window onto the cathode. The tube also is provided with a target electrode l4 located at one end thereof adjacent the window l2. The target electrode is provided with a relatively small aperture i5, substantially of the size of an elemental area of the picture which it is desired to analyze. Preferably the aperture is located on the central axis of the tube. In any case, it faces the cathode l3, so that electrons from the cathode may enter the target electrode through the scan ning aperture it. In accordance with generally preferred practice, the target electrode l4 serves as a housing for an electron multiplier, whereby a preliminary video signal amplification may be enfected. The target electrode also is maintained at a positive potential relative to the cathode by means such as a battery It.

The tube l I also is provided with a plurality of elongated deflecting electrodes such as the wires or rods 5?. In the embodiment of the invention disclosed herein the tube is provided with twelve of such electrodes uniformly spaced around the inside periphery of the envelope. These electrodes extend parallel to the longitudinal axis of the tube and preferably from the plane of the cathode 3 to a plane adjacent to the scanning aperture E5 of the target electrode M. Each of the electrodes is connected through the tube envelope by means, such as a conductor l8. In this manner electrical connections may be made to each of the electrodes. An electrically conducting wall coating 19 is formed on the inside of the tube envelope. This wall coating may be connected to the anode id, as shown.

The tube is also provided with an electron focusing device such as an electromagnetic coil 28 which is mounted around the exterior portion of the tube envelope in such a manner that it substantially completely encloses the space between the cathode l3 and the target electrode 14. The focusing coil may be energized from a suitable source of unidirectional voltage such as a battery 2% which may be connected to the coil through an adjustable resistor 22. By means of this resistor the magnitude of the current flowing through the focusing coil may be varied so as to eiiect the desired focusing of the electron beam.

The electrical connections to the field producing electrodes such as H are indicated in Fig. 2 to which reference will now be made. In the drawing which includes a transverse sectional view of the image dissector tube I I, there are shown completely the connections between each of the tube electrodes and the voltage distributing system, whereby beam orientation is obtained. Inasmuch as the facilities required for the impression of the deflecting voltages upon these electrodes forms no part of the instant invention, the connections to the tube electrodes for this purpose have been shown only diagrammatically.

Each of the field-producing electrodes of the tube is connected through one of a plurality of resistors 23 to one of a plurality of contacts of a multi-pole multi-position switch 24. This switch is also provided with contact arms which are connected to suitable taps on a voltage divider 25. The voltage divider comprises a series connection of a plurality of resistors such as 26 and 217 having impedance values suitable to provide the desired distribution of the energizing voltage. The voltage divider is energized from a. source of unidirectional voltage such as a battery 28. Two potentiometers, 29 and 3| are connected to the terminals of the battery 28. The sliding contact 32 of the potentiometer 29 is connected through a resistor 33 to one terminal of the voltage divider 25. The sliding contact 34 of the other potentiometer 3| is connected through a resistor 35 to the other terminal of the voltage divider.

The particular form of the switch 24 which is employed in practicing the invention is immaterial. Many switches for the purpose are well known in the art and no attempt is made in the instant disclosure to indicate any particular type of switch. The arrangement shown is purely diagrammatical and is for the purpose of illustrating the invention in the simplest possible manner. As-shown, the switch 24 comprises a plurality of contacts, such as 36, equally spaced in a circular pattern. There also are provided an equal number of contact arms, such as 31, designed to engage any one of the contacts such as 36. Connections are made between the contact arms and the taps on the voltage divider by any suitable means. For example, a connection is made from the voltage divider tap 38 at the junction point of resistors 26 and 2'! to the contact arm 31 by means of a ''conductor 39. Similar connections are made to the other contact arms of the switch as shown. Two of the contact arms El and Mare connected re spect-ively to the terminals of the voltage divider 2-5. The other contact arms are connected in pairs to the intermediate taps on the voltage divider. For example, the contact arm 37 and the contact arm 43 are connected together internally of the switch, whereby both are connected by the conductor 39 to the voltage divider tap 33.

For the impression of the deflecting voltage upon the field producingelectrodes such as H of the tube H, couplings are provided 'from'the re spective electrodes to a voltage distribution system for the deflecting voltages. For example, the electrode 3 3 is coupled by a condenser to the deflecting voltage distributing network 53. The high frequency deflecting voltage source t! is coupled to two terminals of the distribution network and the low frequency deflecting voltage source -58 is connected to a-nother pair of input terminals of the distribution network. Both of these deflecting voltages vary periodically in a saw-tooth wave manner, whereby the voltages derived from the network -43 for impression upon the tube electrodes are varied according to a saw-tooth form. The'voltage distribution network 35 has the characteristic of properly proportioning the saw-tooth voltages so that they are impressed upon the tube electrodes in proper magnitudes to produce a dc fiectin'g field of substantially uniformintensity.

Referring now to the operation of the voltage distributing system in accordance with the present invention, assume that it is desired to center the electron beam at the scanning aperture of the anode electrode. Also assume that the scanning aperture is located on the longitudinal axis of the tube. Assume also that the electron beam is initially centered below and to the left of the long'i-- tudinal axis of the tube as it is viewed in Fig. 2. In such a case the switch 24 is manipulated so as to effect such a movement of the contact arms relative to the contacts of the switch that the positions are as shown in the drawing. In such a case the contact arm 42 by its engagement with the contact 49 connects the lower terminal of the voltage divider 25 to the tube electrode 5 l At the same time the contact arm 4! by its engagement with the contact 52 connects the upp terminal of the voltage divider to the tube-electrode 53. 'In this manner the voltage of greatest magnitude which may be derived fromthe voltage divider 25 is connected to the diametrically opposed electrodes 5| and 53. The voltages which are impressed upon all other electrodes of the tube are of lesser magnitudes by reason of the connections of these electrodes through the switch 24 to intermediate taps on the voltage divider. Electrodes 5E and 55 are connected to the center tap 56 of the voltage divider and, therefore, are at zero potential. It may be seen, therefore, that the field which is produced by the tube electrodes for orienting the electron beam is angularly directed relative to the vertical aXis of the tube, so that it extends along the line joining the electrodes 5i and 53. If now the sliders 32 and 3d of the potentiometers 29 and 3! respectively are moved downwardly below the center points of the potentiome ters, a positive potential will be impressed upon electrode 53 and an equal negative potential will be impressed upon the electrode 5!. The other tube electrodes will have positive and negative potentials impressed thereon to produce the desired field which will tend to shift the electron beam upwardly along the line joining the electrodes 5| and 53. The magnitude of the beam shift will depend upon the magnitude of the-centering voltages applied to the tube electrodes. These are regulated by'the potentiometersz and '31.

It may be seen from the foregoing description of an illustrative embodiment of the invention that the direction of the beam centering field is determined by the position of the switch 2d. The

strength of this field may be varied by the potentiometers 29 and 3t The effect of such a system is to produce a beam centering facility which operates on t 1e basis of polar coordinates in contrast to more conventional systems operating on the basis of rectilinear coordinates. An advantage or" such a system is that there is no need to provide a complex voltagedistribution network, such as that disclosed in the co-pending Salinger application referred to where the beam centering is effected according to rectilinear coordinates. In a system-embodying the present invention only one voltage varying piece of apparatus is required. Consequently, the power losses inherent the use of such devices are considerably lower.

in general, it is seen that the voltage divider 25 is an illustrative embodiment of a voltage distributing network for deriving from a source of unidirectional voltage a predeterminedvoltage distribution pattern for the field-producing electrodes. The switch 21.: is one device for efiecting a cyclical permutation of the electrodes with respect to the voltage distribution pattern. That is, the electrodes maybe shifted in their connec tions to the network without changing the order orse uenoe of the electrodes.

While there has been described what at presentis considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is aimed, therefore, in the apended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A system for orienting an electron beam relative to a target electrode comprising, .a plurality of field-producing electrodes located in spaced positions around the path of said beam, a source of unidirectional voltage, a voltage distributing network for deriving from said source a predetermined voltage distribution pattern for said electrodes, a switch for connecting said electrodes to said voltage distributing network and adapted to eiiect a cyclical permutation of said electrodes with respect to said voltage distribution pattern, whereby to secure any one of a plurality of angular directions of the field produced by said electrodes in the path of said beam, and means to vary the magnitude of the voltage impressed upon said voltage distributing network from said source, whereby to correspondingly vary the strength of said field.

2. A system for orienting an electron beam relative to a target electrode comprising, a plurality of elongated field-producing electrodes located in spaced positions around the path of said beam, a voltage distributing network, a switch connecting said field-producing electrodes to said voltage distributing network, said switch being adapted to connect said electrodes to any one of a plurality of different voltage points on said voltage distributing network, whereby to secure any one of a plurality of angular directions of the field produced by said electrodes in the path of 7 said beam, and means to variably energize said voltage distributing network, whereby to correspondingly vary the strength of said field.

3. A system for orienting an electron beam relative to a target electrode comprising, a plurality of elongated field-producing electrodes located in spaced positions around the path of said beam, a voltage distributing network, a multi-- pole multi-position switch connecting said fieldproducing electrodes to said voltage distributing network, said switch. being operable to change the connections of said electrodes to said voltage distributing network so as to shift the angular direction of the field produced by said electrodes inrthe path of said beam, a source of unidirectiona1 voltage coupled to said voltage distributing network, and means to vary the magnitude of the voltage impressed upon said voltage distributing network, whereby to correspondingly vary the strength of said field.

4. A system for orienting an electron beam relative to a target electrode comprising, a plurality of elongated field-producing electrodes located in spaced positions circularly around the path of said beam, a voltage distributing network having a plurality of different voltage taps, a switch having two sets of contacts, means for connecting one set of said switch contacts respectively to said field-producing electrodes, means for connecting the other set of said switch contacts to said voltage distributing network taps, one set of said switch contacts being operable relative to the other set of said contacts to change the connections of said electrodes to said voltage distributing network taps so as to shift the angular direction of the field produced by said electrodes in the path of said beam, a source of unidirectional voltage coupled to said voltage distributing network, and means to vary the magnitude of the voltage impressed upon said voltage distributing network, whereby to correspondingly vary the strength of said field.

5. A system for orienting an electron beam relative to a target electrode comprising, a plurality of elongated field-producing electrodes lo. cated in spaced positions circularly around the path of said beam, a voltage divider having a plurality of different voltage taps, a switch having two sets of contacts each equal in number to the number of said field-producing electrodes, means for connecting one set of said switch contacts respectively to said field-producing electrodes, means for connecting the other set of said switch contacts to said voltage divider taps, one set of said switch contacts being operable relative to the other set of said contacts to change the connections of said electrodes to said voltage divider taps so as to shift the angular direction of the field produced by said electrodes in the path of said beam, a source of unidirectional voltage coupled to respective terminals of said voltage divider, and means to Vary the magnitude of the voltage impressed upon said voltage divider, whereby to correspondingly vary the strength of said field.

6. A system for orienting an electron beam relative to a target electrode comprising, a plurality of elongated field-producing electrodes located in spaced positions circularly around the path of said beam, a voltage divider having a plurality of diiferent voltage taps, a switch having a set of stationary contacts and a corresponding set of movable contacts equal in number to the number of said field-producing electrodes, means for connecting one set of said switch contacts respectively to said field-producing electrodes, means for connecting the other setof said switch contacts to selected ones of said voltage divider taps, said movable switch contacts being operable relative to said stationary contacts to change the connections of said electrodes to said voltage divider taps so as to shift the angular direction of the iield produced by said electrodes in the path of said beam, a source of unidirectional voltage, and means including a pair of voltage varying devices for coupling said voltage source to respective terminals of said voltage divider, said voltage varying devices being adjustable to vary the magnitude of the volt-age impressed upon said voltage divider, whereby to correspondingly vary the strength of said field.

7. A system for orienting an electron beam relative to a target electrode comprising, a plurality of elongated field-producing electrodes located in spaced positions circularly around the path of said beam, a voltage divider having a plurality of difierent voltage taps, a switch having a plurality of contacts and a corresponding number of movable arms equal in number to the number of said field-producing electrodes, means for connecting said switch contacts respectively to saidfield-producing electrodes, means for connecting said switch arms to selected ones of said voltage divider taps, said switch arms being operable relative to said contacts to change the connections of said electrodes to said voltage divider taps so as to shift the angular direction of the field produced by said electrodes in the path of said beam, a source of unidirectional voltage, and means including a pair of potentiometers for coupling said voltage source to respective terminals of said voltage divider, said potentiometers being adjustable to vary the magnitude of the voltage impressed upon said voltage divider, whereby to correspondingly vary the strength of said field.

HANS W. G. SALINGER. ALBERT T. MAYLE, J R. 

